I agree the Service’s bios of Lenin, Trotsky and Stalin are very good - perhaps the best single volume English language bios of Lenin and Trotsky available.
I also highly recommend Orlando Figes’ A People’s Tragedy for a good read on the 30 year period leading up to the Bolshevik coup in October 1917. I have heard but not read, that Antony Beevor’s recently published survey of the Russian Revolution is also very good. Beevor, like Figes, is immensely readable and always well researched and organised.